Device and method for detecting paper sheets

ABSTRACT

The apparatus has at least one optical sensor ( 7, 8 ), which emits a light beam ( 13, 14 ), inclined at an angle in relation to the surface of the pallet ( 2 ), and irradiates the surface of the pallet ( 2 ) at a point of reflection, and supports ( 9, 10 ) with cylinders for displacing the point of reflection by a predetermined distance over the surface of the pallet ( 2 ).

BACKGROUND OF THE INVENTION

The present invention relates to a device which makes it possible todetect the presence and the position of a ream of paper sheets, inparticular sheets of securities or banknotes, on pallets. The presentinvention also relates to a method for such a detecting operation.

A problem which is frequently encountered in the production of printedsheets is the precise positioning of the sheet stacks on the pallets.This is because, in the case of a process for printing paper sheets, forexample for securities or banknotes, sheet stacks are often transportedon pallets from one machine to the other in order to run through thevarious steps of the process. It is thus the case that a sheet stack isfed to a given machine on a pallet and transferred into the inlet of themachine, the sheets ale introduced individually into the machine, inorder for it to be possible for the machine to carry out its processstep, for example printing, numbering or the like, and the sheet stackis reinstated on a pallet at the outlet of the machine.

In the case of an industrial production process, it is, of course, thecase that, rather than just a single pallet being fed to the inlet of amachine, a continuous flow of pallets and sheet stacks is guided to andfrom each machine.

While the formation of sheet stacks at the outlet of a machine isstraightforward, each sheet which has been processed by the machinepassing out individually, it is more complicated for sheet stacks to betransferred from pallets to the inlet of the machine.

The sheets stacked up in a pallet have to be reliably transferred fromthe pallet to the feed table of the machine. This transfer operationcall take place in various various for example, the pallet can bearranged on a feed table, on which the pallet is located in a knownreference position of a transfer system; the transfer system, whichcomprises in particular a suitable gripper system for gripping the sheetstack, can be fed; a crosspiece can be lowered, in order for the palletto be connected to the feed table of the machine, and the stack can beconveyed from the pallet to the feed table.

At this stage, it has appeared necessary to carry out sensing of thepresence and of the position of the sheet stack on the pallet. This isbecause, if there is no sheet located on the pallet, it is necessary toavoid the above-described transfer process and to change the palletinstead and, if the sheet stack is positioned incorrectly on the pallet,for example if it is located too close to the border of the pallet onwhich the crosspiece is supported or if it is oriented obliquely, it mayobstruct the movement of the crosspiece, which will then result inmachine blockage and renders the intervention of an operator necessary.In the case of an industrial production process, such time losses arenot acceptable and have to be reduced to a minimum.

Nevertheless, precise and reliable detection of the presence and/or ofthe position of a sheet stack on a pallet raises numerous problems.

A first problem is that it may be the case that the sheet stacks aresupplied on pallets made of different material. It is thus possible forstacked sheets to be received on pallets made of metal, for example ofsteel, which have a reflective surface, or on pallets made of plastic,which have a matt surface. The sensing system thus has to be capable ofsensing the presence of sheets or sheet stacks irrespective of the typeof pallet used, each type of pallet, for this reason, having a differentreflection coefficient.

A second problem is that sheets printed in different colors may affectthe performance of the sensing system used: since the different colorshave a different reflection behavior, it is possible that the sensingsystem may not be able to sense the presence of sheets on a givenpallet.

Finally, where securities or banknotes are concerned, holograms areoften used as a security element. A hologram, however, likewise appearsto affect the performance of the sensing system. On account of theparticular reflection behavior of a hologram, it may be the case thatthe sensor used does not sense the presence of sheets, to be precise inparticular if the sensing operation takes place at the location wherethe hologram is situated. It is difficult, or even impossible, for thesensor to be reliably adjusted for definite sensing.

SUMMARY OF THE INVENTION

The object of the invention is thus to develop a device and a methodwhich are reliable and are not influenced by external parameters, forexample the material of the pallets, the color of the print or thepresence of security elements, for example holograms or the like, onimprints.

This object is achieved by the device and the method defined in theclaims.

Since the optical sensors emit a light beam which is inclined inrelation to the surface of the pallet and are displaced by a certaindistance, it is possible to avoid the problems caused by the material ofthe pallets and the colors used for printing.

The invention has numerous advantages, and it may be mentioned, inparticular, that the apparatus is easy to produce and reliable to use.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood by way of the description of inembodiment thereof and the figures relating thereto.

FIG. 1 shows a front view of a device according to the invention.

FIG. 2 shows a side view of the device according to FIG. 1.

FIG. 3 shows a plan view of the device according to FIG. 1.

FIG. 4 shows a block diagram of the process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The apparatus will be described first of all with reference to FIG. 1.

This figure illustrates a sheet stack 1 on a pallet 2, the pallet 2being arranged on an aligning table 3. Provided above the stack 1 is aframe 4, which can be lowered and raised again above the stack. Thisframe 4 supports, in particular, a gripper system 5, which can move thepallets, and a detecting system. The detecting system comprises twooptical sensors 7 and 8, which are fastened on the supports 9 and 10.The Supports 9 and 10, in turn, are fastened on the frame 4 by means ofcompressed-air cylinders 11 and 12 (see FIG. 3), which allow the opticalsensors 7 and 8 to move between a starting position and an end position.This end position is illustrated schematically in FIG. 3 by the opticalsensors 7′ and 8′. The distance between the starting position and theend position may be adjusted by moveable stops. It is thus possible forthe system to be adapted to different sizes of hologram. The opticalsensors 7 and 8 each emit a light beam 13 and 14 of which the reflectionon the pallet 2 is used for the sensing operation. The sensors 7 and 8each emit a light beam 13, 14 which rather than running perpendicularlyto the surface of the sheets of the stack 1, that is to say of thepallet 2, is angled, preferably by 40°, in relation to the surface ofthe stack, in order not to be adversely affected by the differentreflection coefficients of the pallets, or by the color of the prints onthe paper.

FIG. 2 illustrates, in particular, the sensor 7 with its beam 13 in thestarting position and the sensor 8′ with its beam 14′ in the endposition. FIG. 2 also shows a crosspiece 15, which pivots about the axis16 in order to allow it to be positioned on the pallet 2 and to allowtransfer of the sheet stack 1 to the feed table 17 of the machine.

In the situation illustrated in FIG. 2, the sheet stack 1 has beenoffset to the right on the pallet 2, that is to say in the direction ofthe crosspiece 15, and the latter cannot be lowered properly. Thedetection takes place as follows: the sensors 7 and 8 are aligned withthe border of the pallet 2 in their starting position. The sensors areswitched on in order to emit their respective beams 13 and 14, and theyare then displaced laterally by means of the cylinders 11 and 12, withthe result that they arrive in an aligned manner in the end position,which is illustrated symbolically by the sensor 8′ in FIG. 2. Whilesensing the presence of the stack 1 during the displacement of thesensors between two reference positions, it is easily possible toestablish whether the sheet stack 1 is located in an acceptable positionor whether it is located too close to the border of the pallet 2.

In exactly the same way as it is detected whether the sheet stack 1 hasbeen displaced on the pallet, it is also possible, by means of thepresent invention, to establish whether one or more sheets of the stack1 project and may possibly obstruct the positioning of the crosspiece15.

It is, of course, necessary for the above-described apparatuses to beassigned to position sensors, in particular for the compressed-aircylinders 11 and 12, and to a central electronic-management unit, whichmakes it possible to analyze the data received from the optical sensors,to track the movement of said sensors between their reference positions(the starting position and the end position) and to produce a suitablecontrol signal in dependence on the detection which has taken place, forexample an error signal it the stack 1 is positioned incorrectly and acontrol signal for continuing the process (for example lowering thecrosspiece 15) if the stack 1 is located in an acceptable position. Thislist of control signals is obviously not exhaustive and depends on theapparatus in question. It would also be possible, for example, to usethe gripper system 5 for correcting the position of the stack 1 if thelatter is located too close to the border of the pallet 2. For thispurpose, the signals produced by the optical sensors can be used inorder to calculate the displacement necessary for correction purposes,and the sensors can then confirm the correction which has been carriedout.

Different types of apparatuses may be assigned to end stops in order tosense the arrival of the sensors, for example proximity sensors or thelike.

The method according to the invention is illustrated in the blockdiagram according to FIG. 4 and comprises the following steps:

-   -   switching on the sensor,    -   displacing the sensor by a predetermined distance.    -   continuously analyzing the reflected light signal for sensing        the presence of sheets,    -   stopping the sensor at the end of the path,    -   emitting a suitable signal in dependence on the sensing result,    -   switching off the sensors and guiding the sensors back into        their starting position.

The inclination of the light beams in relation to the surface of thesheets is preferably 40°. Slight deviations from this value are, ofcourse, possible.

Furthermore, the example described contains two sensors in order for itlikewise to be possible to sense a sheet stack which is orientedobliquely on the pallet.

Furthermore, the length of the path over which the sensors are displaceddepends on the imprints located on the sheets. In particular, as hasbeen seen above, it is necessary, if the imprints contain a hologram andif the light beam comes into contact with the hologram, to cover a path% which is of a greater dimension in the displacement direction than thehologram, in order to move past the latter and to carry out thedetection operation over a part of the sheet which does not contain anyhologram. This path could thus be shorter if the sheets do not containany hologram, and time could thus be saved during this step.

Of course, other modifications are also possible within the scope of theinvention.

Although illustrative embodiments of the invention have been shown anddescribed, a wide range of modification, change and substitution iscontemplated in the foregoing disclosure and in some instances, somefeatures of the present invention may be employed without acorresponding use of the other features. Accordingly, it is appropriatethat the appended claims be construed broadly and in a manner consistentwith the scope of the invention.

1. A device for detecting the presence of paper sheets (1), inparticular sheets of securities or banknotes, on a pallet (2), whereinthe device has at least one optical sensor (7, 8), which emits a lightbeam (13, 14), inclined at an angle in relation to the surface of thepallet (2), and irradiates the surface of the pallet (2) at a point ofreflection, and means (9, 10, 11, 12) for displacing the point ofreflection by a predetermined distance over the surface of the pallet(2).
 2. The device as claimed in claim 1, wherein the angled inclinationis approximately 40°.
 3. The device as claimed in claim 2, wherein itcontains two symmetrical sensors (7, 8).
 4. The device as claimed inclaim 4, wherein the means which allow the point of reflection to bedisplaced are formed at least by a compressed-air cylinder (11, 12)which acts on a support (9, 10), on which each sensor (7, 8) isfastened, such that the sensor (7, 8) is displaced parallel to thesurface of the pallet.
 5. The device as claimed in one of the precedingclaims, wherein the displacement takes place over a predetermineddistance.
 6. A method for detecting a ream of paper, in particular aream of securities or banknotes, on a pallet by means of at least oneoptical sensor which emits a light beam onto a point of reflection, theprocess comprising the following steps: switching, on the sensor,displacing the point of reflection, analyzing the reflected light signalfor sensing the presence of sheets, stopping the movement of the pointof reflection, emitting a suitable signal in dependence on the sensingresult, switching off the sensor.
 7. The method as claimed in claim 6,wherein the displacement of the point of reflection takes place bylinear displacement of the sensor by a predetermined distance runningparallel to the surface of the pallet.
 8. The method as claimed in claim7, wherein the predetermined distance is greater than the dimension of ahologram provided on the paper.
 9. The method as claimed in claim 6,wherein it uses two symmetrical sensors.